/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.context.request.async;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.Consumer;

import javax.servlet.AsyncContext;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.util.Assert;
import org.springframework.web.context.request.ServletWebRequest;

/**
 * A Servlet 3.0 implementation of {@link AsyncWebRequest}.
 *
 * <p>The servlet and all filters involved in an async request must have async
 * support enabled using the Servlet API or by adding an
 * {@code <async-supported>true</async-supported>} element to servlet and filter
 * declarations in {@code web.xml}.
 *
 * @author Rossen Stoyanchev
 * @since 3.2
 */
public class StandardServletAsyncWebRequest extends ServletWebRequest implements AsyncWebRequest, AsyncListener {

    private Long timeout;

    private AsyncContext asyncContext;

    private AtomicBoolean asyncCompleted = new AtomicBoolean(false);

    private final List<Runnable> timeoutHandlers = new ArrayList<>();

    private final List<Consumer<Throwable>> exceptionHandlers = new ArrayList<>();

    private final List<Runnable> completionHandlers = new ArrayList<>();


    /**
     * Create a new instance for the given request/response pair.
     *
     * @param request  current HTTP request
     * @param response current HTTP response
     */
    public StandardServletAsyncWebRequest(HttpServletRequest request, HttpServletResponse response) {
        super(request, response);
    }


    /**
     * In Servlet 3 async processing, the timeout period begins after the
     * container processing thread has exited.
     */
    @Override
    public void setTimeout(Long timeout) {
        Assert.state(!isAsyncStarted(), "Cannot change the timeout with concurrent handling in progress");
        this.timeout = timeout;
    }

    @Override
    public void addTimeoutHandler(Runnable timeoutHandler) {
        this.timeoutHandlers.add(timeoutHandler);
    }

    @Override
    public void addErrorHandler(Consumer<Throwable> exceptionHandler) {
        this.exceptionHandlers.add(exceptionHandler);
    }

    @Override
    public void addCompletionHandler(Runnable runnable) {
        this.completionHandlers.add(runnable);
    }

    @Override
    public boolean isAsyncStarted() {
        return (this.asyncContext != null && getRequest().isAsyncStarted());
    }

    /**
     * Whether async request processing has completed.
     * <p>It is important to avoid use of request and response objects after async
     * processing has completed. Servlet containers often re-use them.
     */
    @Override
    public boolean isAsyncComplete() {
        return this.asyncCompleted.get();
    }

    @Override
    public void startAsync() {
        Assert.state(getRequest().isAsyncSupported(),
                "Async support must be enabled on a servlet and for all filters involved " +
                        "in async request processing. This is done in Java code using the Servlet API " +
                        "or by adding \"<async-supported>true</async-supported>\" to servlet and " +
                        "filter declarations in web.xml.");
        Assert.state(!isAsyncComplete(), "Async processing has already completed");

        if (isAsyncStarted()) {
            return;
        }
        this.asyncContext = getRequest().startAsync(getRequest(), getResponse());
        this.asyncContext.addListener(this);
        if (this.timeout != null) {
            this.asyncContext.setTimeout(this.timeout);
        }
    }

    @Override
    public void dispatch() {
        Assert.notNull(this.asyncContext, "Cannot dispatch without an AsyncContext");
        this.asyncContext.dispatch();
    }


    // ---------------------------------------------------------------------
    // Implementation of AsyncListener methods
    // ---------------------------------------------------------------------

    @Override
    public void onStartAsync(AsyncEvent event) throws IOException {
    }

    @Override
    public void onError(AsyncEvent event) throws IOException {
        this.exceptionHandlers.forEach(consumer -> consumer.accept(event.getThrowable()));
    }

    @Override
    public void onTimeout(AsyncEvent event) throws IOException {
        this.timeoutHandlers.forEach(Runnable::run);
    }

    @Override
    public void onComplete(AsyncEvent event) throws IOException {
        this.completionHandlers.forEach(Runnable::run);
        this.asyncContext = null;
        this.asyncCompleted.set(true);
    }

}
